Particulate matter, or PM, is the term for particles found in the air including, e.g., dust, dirt, soot, smoke, and liquid droplets. PM2.5 generally refers to particles with a diameter less than or equal to 2.5 micrometers, and may have a significant impact on air quality, visibility, etc. For example, PM2.5 may be suspended in the air for a long time, and the higher the concentration of PM2.5 in the air, the more severe the air pollution is.
Conventionally, air purifiers may be used to reduce PM2.5 in the air.